Viscoelastic behaviour of vinylic copolymers of cellulose and their glass transition temperature by DSC

Abstract

AbstractThe viscoelastic response of some vinylic copolymers of cellulose prepared with vinyl acetatemethyl acrylate mixtures and with Ce(IV) ion as initiator, and native cellulose, were studied at 110 Hz in a range of temperatures from −120–100°C.The viscoelastic spectrum of cellulose shows the β‐relaxation that is not shown in its vinylic copolymers. We observed the same effect in the dielectric β‐relaxation.For the vinylic copolymers of cellulose, one viscoelastic relaxation attributed to the α‐relaxation of the grafted vinylic chains is observed. Some differences in the characteristics of this relaxation may be related to the composition of PVA/PMA vinylic side chains and to the ratio of cellulose in the copolymer. The plots of the Argand diagrams give us a better understanding of the viscoelastic behaviour of these materials. The results seem to indicate that the cellulose hinders the large‐scale motions of the vinylic chains grafted onto it. The glass transition temperature (Tg) determined by differential scanning calorimetry (DSC) also shows the same fact: the Tg of the vinylic copolymers of cellulose are higher than both the Tg of polyvinyl acetate–polymethyl acrylate copolymers (PVA–PMA) without cellulose and the Tg of some blends of cellulose and the PVA–PMA whose composition was as similar as possible to the cellulosic copolymers. The importance of the covalent bonds between cellulose and the vinylic side chains in the structural transitions are revealed. The present results are compared with the dielectric α‐relaxation that we described elsewhere. © 1993 John Wiley & Sons, Inc.